<html>
<head>
	<meta charset="UTF-8">
	<meta content="IE=edge" http-equiv="X-UA-Compatible">
	<meta content="initial-scale=1.0, maximum-scale=1.0, user-scalable=no, width=device-width" name="viewport">
	<title>2981：[Poi2002]括号</title>
	<!-- css -->
	<link href="../css/base.min.css" rel="stylesheet">
	<link href="../css/project.min.css" rel="stylesheet">
	
	<!-- favicon -->
	<!-- ... -->
</head>
<body class="page-brand">
	<header class="header header-transparent header-waterfall ui-header">
		<ul class="nav nav-list pull-left">
			<li>
				<a data-toggle="menu" href="#menu">
					<span class="icon icon-lg">menu</span>
				</a>
			</li>
		</ul>
		<a class="header-logo header-affix-hide margin-left-no margin-right-no" data-offset-top="213" data-spy="affix">[Poi2002]括号</a>
		<span class="header-logo header-affix margin-left-no margin-right-no" data-offset-top="213" data-spy="affix">[Poi2002]括号</span>
	</header>
	<nav aria-hidden="true" class="menu" id="menu" tabindex="-1">
		<div class="menu-scroll">
			<div class="menu-content">
				<a class="menu-logo" href="../index.html">BZOJ离线题库</a>
				<ul class="nav">
					<li>
						<a class="waves-attach" data-toggle="collapse" href="#problems">题目</a>
						<ul class="menu-collapse collapse in" id="problems">
							<li>
								<a class="waves-attach" href="../index.html">主页</a>
							</li>
							<li>
								<a class="waves-attach" href="../list.html">题目列表</a>
							</li>
						</ul>
					</li>
					<li>
						<a class="collapsed waves-attach" data-toggle="collapse" href="#about">关于</a>
						<ul class="menu-collapse collapse" id="about">
							<li>
								<a class="waves-attach" href="../about.html">关于此项目</a>
							</li>
						</ul>
					</li>
					
				</ul>
			</div>
		</div>
	</nav>
	<main class="content">
		<div class="content-header ui-content-header">
			<div class="container">
				<h1 class="content-heading">
                [Poi2002]括号                </h1>
                <p>时间限制：1s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：128MB</p>			</div>
		</div>
		<div class="container">
			<section class="content-inner margin-top-no">
				<div class="row">
					<div class="col-lg-13 col-md-13">
						<div class="card margin-bottom-no">
							<div class="card-main">
								<div class="card-inner">
									
                                <h3>题目描述</h3><p><div align="center"></div>
<div><span style="font-size: medium">减法不满足结合率, 例如 (5-2)-1=2, 但 5-(2-1)=4, 因此 (5-2)-1&lt;&gt;5-(2-1). 这意味着表达式5-2-1 依赖减法操作的顺序. 如果没有扩号，假定表达式计算从左到右, 即5-2-1 等于 (5-2)-1.我们给出表达式的形式如下：</span></div>
<div align="center"><span style="font-size: medium"><i>x</i><sub>1</sub> +/- <i>x</i><sub>2</sub> +/- ... +/- <i>x<sub>n</sub></i>,</span></div>
<div><span style="font-size: medium">+/- 表示+ (加)&nbsp;- (减), <i>x</i><sub>1</sub>,<i>x</i><sub>2</sub>,...,<i>x<sub>n</sub></i> 表示计算变量. 对下面的表达式</span></div>
<div align="center"><span style="font-size: medium"><i>x</i><sub>1</sub>-<i>x</i><sub>2</sub>-...-<i>x<sub>n</sub></i></span></div>
<div><span style="font-size: medium">我们想插入<i>n</i>-1对括号得到和表达式相同的结果.例如，我们想得到和下面表达式相等值的表达式 </span></div>
<div align="center"><span style="font-size: medium"><i>x</i><sub>1</sub>-<i>x</i><sub>2</sub>-<i>x</i><sub>3</sub>+<i>x</i><sub>4</sub>+<i>x</i><sub>5</sub>-<i>x</i><sub>6</sub>+<i>x</i><sub>7</sub></span></div>
<div><span style="font-size: medium">可以对下面的表达式插入括号</span></div>
<div align="center"><span style="font-size: medium"><i>x</i><sub>1</sub>-<i>x</i><sub>2</sub>-<i>x</i><sub>3</sub>-<i>x</i><sub>4</sub>-<i>x</i><sub>5</sub>-<i>x</i><sub>6</sub>-<i>x</i><sub>7</sub></span></div>
<div><span style="font-size: medium">得到</span></div>
<div align="center"><span style="font-size: medium">(((<i>x</i><sub>1</sub>-<i>x</i><sub>2</sub>)-((<i>x</i><sub>3</sub>-<i>x</i><sub>4</sub>)-<i>x</i><sub>5</sub>))-(<i>x</i><sub>6</sub>-<i>x</i><sub>7</sub>)).</span></div>
<div><span style="font-size: medium"><b>注意:</b> 我们只对完整而正确的表达式有兴趣，一个完整正确的表达式必须符合</span></div>
<ul type="disc">
    <li><span style="font-size: medium">它可能是单个变量, </span></li>
    <li><span style="font-size: medium">可能形如(<i>w</i><sub>1</sub>-<i>w</i><sub>2</sub>), 而且 <i>w</i><sub>1</sub> 和 <i>w</i><sub>2</sub> 都是完成而正确的表达式. </span></li>
</ul>
<div><span style="font-size: medium">通常来说，我们对如下空括号形式不感兴趣: (), (<i>x<sub>i</sub></i>), ((...)). 而表达式 <i>x</i><sub>1</sub>-(<i>x</i><sub>2</sub>-<i>x</i><sub>3</sub>) 不是完整的，因为它缺少最外层的括号.</span></div></p><hr/><h3>输入格式</h3><p><div style="margin: auto 0cm"><span style="font-size: medium">第一行有一个整数 <i>n</i>, 2&lt;=<i>n</i>&lt;=1&nbsp;000&nbsp;000. 表示表达式变量的个数.在下面的 <i>n</i>-1 行有一个字符<tt>+</tt> 或 <tt>-</tt>. 第<i>i</i>行 出现的字符给出了<i>x<sub>i</sub></i><sub>-1</sub> 和 <i>x<sub>i</sub></i> 之间的操作. </span></div>
<div></div></p><hr/><h3>输出格式</h3><p><div><span style="font-size: medium">对表达式<i>x</i><sub>1</sub>-<i>x</i><sub>2</sub>-...-<i>x<sub>n</sub></i>添加n-1对括号，使得它与给出的表达式等价。在<tt>naw.out</tt> 中写入一个整数，表示插入空格的不同方案数，答案不超过1&nbsp;000&nbsp;000&nbsp;000。</span></div>
<p>
<divre></divre>
</p></p><hr/><h3>样例输入</h3><pre>7
-
-
+
+
-
+


 
</pre><hr/><h3>样例输出</h3><pre>3
</pre><hr/><h3>提示</h3><p>没有写明提示</p><hr/><h3>题目来源</h3><p>没有写明来源</p>
								</div>
							</div>
						</div>
					</div>
				</div>
				
				
			</section>
		</div>
	</main>

	<div class="fbtn-container">
		<div class="fbtn-inner">
			<a class="fbtn fbtn-lg fbtn-brand-accent waves-attach waves-circle waves-light waves-effect" data-toggle="dropdown" aria-expanded="true"><span class="fbtn-text fbtn-text-left">Menu</span><span class="fbtn-ori icon">apps</span><span class="fbtn-sub icon">close</span></a>
			<div class="fbtn-dropup">
				<a class="fbtn fbtn-brand waves-attach waves-circle waves-light waves-effect" href="../list.html" target="_self"><span class="fbtn-text fbtn-text-left">题目列表</span><span class="icon">menu</span></a>
				<a class="fbtn fbtn-green waves-attach waves-circle waves-effect" href="../index.html" target="_self"><span class="fbtn-text fbtn-text-left">返回主页</span><span class="icon">home</span></a>
				<a class="fbtn waves-attach waves-circle waves-effect" href="http://www.lydsy.com/JudgeOnline/submitpage.php?id=2981" target="_blank"><span class="fbtn-text fbtn-text-left">提交代码</span><span class="icon">send</span></a>
				<a class="fbtn fbtn-orange waves-attach waves-circle waves-effect" href="http://www.lydsy.com/JudgeOnline/wttl/wttl.php?pid=2981" target="_blank"><span class="fbtn-text fbtn-text-left">试题讨论</span><span class="icon">chat</span></a>
				
			</div>
		</div>
	</div>

	<!-- js -->
	<script src="../js/jquery.min.js"></script>
	<script src="../js/base.min.js"></script>
	<script src="../js/project.min.js"></script>
</body>
</html>